Abstract: The relationship of the maximum loading strain range with fatigue life was established. Selection of electrons microscope magnifying multiple and measuring size in fatigue fracture fractal measure were studied, and secondary electron lines scanning fractal dimension was successfully applied to measuring of Ti alloy welded joint fracture fractal dimension. The relationship is approximate direct ratio between fatigue fracture fractal dimension and fatigue life. According to established model of fatigue damage fractal evolution on welded joint, The fatigue damage fractal evolution equation of TC11 Ti alloy welded joint was analyzed.